EFFECT OF GRAIN-SIZE ON THE OBSERVED PSEUDOELASTIC BEHAVIOR OF A CU-ZN-AL SHAPE-MEMORY ALLOY

The shape of stress-strain curves for a pseudoelastic copper-based sha pe memory alloy (SMA) has been found to depend strongly on the grain s ize-to-sample thickness ratio (gs/t). Previous investigators have attr ibuted this effect to reduced grain constraint in coarse-grain samples . The present investigation further analyzes the grain constraint effe ct by modeling shape memory alloy stress-strain curves. The model resu lts reveal that varying grain constraint can explain the observed grai n size effect on stress-strain curves. Furthermore, detailed considera tion of the Taylor factor equivalent for Cu-Zn-Al and NiTi shape memor y alloys can explain the opposite curvature of polycrystal stress-stra in curves for these two materials. Finally, several indices of grain c onstraint are analyzed for the Cu-Zn-Al alloy examined in the present investigation and for similar alloys used in previous studies. This ev aluation reveals that both transformation modulus and transformation s tress correlate with gs/t, and each can be used as an index of gain co nstraint.